I was using up2date, and it seemed to hang (that is, wouldn't redraw
the display) for a long time in the package retrieval stage.  I finally
got the following traceback:

Traceback (most recent call last):
  File "/usr/share/rhn/up2date_client/gui.py", line 1862, in doRetrieval
    self.setRetrievalProgress)
  File "/usr/share/rhn/up2date_client/up2date.py", line 330, in getPackage
    buffer = rpcServer.doCall(repos.getPackage, pkg, msgCallback, progressCallback)
  File "/usr/share/rhn/up2date_client/rpcServer.py", line 143, in doCall
    up2dateAuth.updateLoginInfo()
  File "/usr/share/rhn/up2date_client/up2dateAuth.py", line 137, in updateLoginInfo
    loginInfo = login()
  File "/usr/share/rhn/up2date_client/up2dateAuth.py", line 112, in login
    loginInfo = rpcServer.doCall(server.up2date.login, systemId)
  File "/usr/share/rhn/up2date_client/rpcServer.py", line 117, in doCall
    log.log_me("A socket error occurred: %s, attempt #%s" % (
  File "/usr/share/rhn/up2date_client/up2dateLog.py", line 31, in log_me
    self.write_log(s)
  File "/usr/share/rhn/up2date_client/up2dateLog.py", line 42, in write_log
    log_file = open(log_name, 'a')
IOError: [Errno 24] Too many open files: '/var/log/up2date'

Looking in /proc/<pid>/fd, I only see 8 file descriptors open, but
of course this is after the fact.